Nowadays, the potentiality of magnetic nanoparticles for a large range of biomedical applications is largely claimed and demonstrated, but their use is conditioned by the possibility to guarantee biocompatibility, actually. For this purpose, an investigated solution is coating them with a polymeric or inorganic shell, such as SiO2 or Au. An alternative approach is exploiting a highly biocompatible material such as hydroxyapatite (HA) [Ca5(PO4)3OH], which is the inorganic component of many biological hard tissues, i.e. bone and teeth. The synthesis of composite materials consisting of magnetic nanoparticles and HA is especially appealing for prospective uses in the field of bone tissue engineering, as the magnetic nanoparticles may act as drug carriers, favoring the tissue regeneration, and allow a controlled drug release under a magnetic or thermal stimulus, possibly exploiting their ability as hyperthermia agents. In this context, we report about a two-step chemical synthesis process of a novel nanogranular system consisting of magnetite nanoparticles embedded in a matrix of biomimetic HA, hence with great potentiality as biocompatible magnetic material. In the first step, Fe(SO4), Fe2(SO4)3 and a strong excess of Tetrabutilammonium hydroxide (TBAOH), acting as surfactant, are refluxed in aqueous solution. This leads to the formation of magnetite nanoparticles, which, in the second step, are coated with a Ca(OH)2 layer to induce the growth of HA directly on their surface, by successive reaction of Ca(OH)2 with HPO42-. Two nanogranular samples have been collected, differing for the magnetite content of ~ 0.8 wt % and 4 wt.%. The as-prepared magnetite nanoparticles and the composite material have been investigated by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. This analyses have allowed us to estimate the mean size of the magnetite nanoparticles (~ 6 nm) and to reveal the presence of hydroxyl groups on their surface. The hydroxyl groups hinder the intimate contact among the nanoparticles and promote the subsequent growth of the carbonate HA phase, featuring a nanocrystalline lamellar structure (platelets dimensions range between 10 and 70 nm). We have measured, by SQUID magnetometer, hysteresis loops at different temperatures in the 5-300 K range, the thermal dependence of the magnetization at different values of the applied magnetic field and the field-dependent isothermal and demagnetized remanence. At T=300 K, both the as-prepared and the HA-coated magnetite nanoparticles are superparamagnetic. However, the magnetization relaxation process is dominated by magnetic interparticle interactions of dipolar nature, which have comparable strength both in the sample of as-prepared magnetite and in the two composite samples, with different magnetite content. In all the three samples, a low-temperature collective frozen magnetic regime is established below T ~ 20 K. These results indicate that the magnetite nanoparticles tend to form agglomerates in the as-prepared state, which are not substantially altered by the subsequent HA growth, coherently with the creation of strong hydrogen bonds among the surface hydroxyl groups.

Synthesis and characterization of magnetic nanogranular Fe3O4/biomimetic hydroxyapatite for potential applications in nanomedicine

SPIZZO, Federico;DEL BIANCO, Lucia
2015

Abstract

Nowadays, the potentiality of magnetic nanoparticles for a large range of biomedical applications is largely claimed and demonstrated, but their use is conditioned by the possibility to guarantee biocompatibility, actually. For this purpose, an investigated solution is coating them with a polymeric or inorganic shell, such as SiO2 or Au. An alternative approach is exploiting a highly biocompatible material such as hydroxyapatite (HA) [Ca5(PO4)3OH], which is the inorganic component of many biological hard tissues, i.e. bone and teeth. The synthesis of composite materials consisting of magnetic nanoparticles and HA is especially appealing for prospective uses in the field of bone tissue engineering, as the magnetic nanoparticles may act as drug carriers, favoring the tissue regeneration, and allow a controlled drug release under a magnetic or thermal stimulus, possibly exploiting their ability as hyperthermia agents. In this context, we report about a two-step chemical synthesis process of a novel nanogranular system consisting of magnetite nanoparticles embedded in a matrix of biomimetic HA, hence with great potentiality as biocompatible magnetic material. In the first step, Fe(SO4), Fe2(SO4)3 and a strong excess of Tetrabutilammonium hydroxide (TBAOH), acting as surfactant, are refluxed in aqueous solution. This leads to the formation of magnetite nanoparticles, which, in the second step, are coated with a Ca(OH)2 layer to induce the growth of HA directly on their surface, by successive reaction of Ca(OH)2 with HPO42-. Two nanogranular samples have been collected, differing for the magnetite content of ~ 0.8 wt % and 4 wt.%. The as-prepared magnetite nanoparticles and the composite material have been investigated by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. This analyses have allowed us to estimate the mean size of the magnetite nanoparticles (~ 6 nm) and to reveal the presence of hydroxyl groups on their surface. The hydroxyl groups hinder the intimate contact among the nanoparticles and promote the subsequent growth of the carbonate HA phase, featuring a nanocrystalline lamellar structure (platelets dimensions range between 10 and 70 nm). We have measured, by SQUID magnetometer, hysteresis loops at different temperatures in the 5-300 K range, the thermal dependence of the magnetization at different values of the applied magnetic field and the field-dependent isothermal and demagnetized remanence. At T=300 K, both the as-prepared and the HA-coated magnetite nanoparticles are superparamagnetic. However, the magnetization relaxation process is dominated by magnetic interparticle interactions of dipolar nature, which have comparable strength both in the sample of as-prepared magnetite and in the two composite samples, with different magnetite content. In all the three samples, a low-temperature collective frozen magnetic regime is established below T ~ 20 K. These results indicate that the magnetite nanoparticles tend to form agglomerates in the as-prepared state, which are not substantially altered by the subsequent HA growth, coherently with the creation of strong hydrogen bonds among the surface hydroxyl groups.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2339031
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